Supercritical fluid-assisted deposition of materials on semiconductor substrates

ABSTRACT

Supercritical fluid-assisted deposition of materials on substrates, such as semiconductor substrates for integrated circuit device manufacture. The deposition is effected using a supercritical fluid-based composition containing the precursor(s) of the material to be deposited on the substrate surface. Such approach permits use of precursors that otherwise would be wholly unsuitable for deposition applications, as lacking requisite volatility and transport characteristics for vapor phase deposition processes.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 11/078,211for “Supercritical Fluid-Assisted Deposition of Materials onSemiconductor Substrates” filed on Mar. 11, 2005 in the name ofChongying Xu et al., which is a divisional of U.S. patent applicationSer. No. 10/303,479 filed Nov. 25, 2002, now U.S. Pat. No. 7,030,168,which claims priority to U.S. Provisional Patent Application No.60/345,738 filed Dec. 31, 2001, all of which are incorporated in theirentirety herein.

FIELD OF THE INVENTION

The present invention relates generally to using supercritical fluids toeffect the deposition of materials on substrates, e.g., semiconductorsubstrates, in the manufacture of semiconductor devices and deviceprecursor structures.

DESCRIPTION OF THE RELATED ART

In the field of semiconductor manufacturing, deposition of materials onsemiconductor substrates is carried out by a variety of techniques,including chemical vapor deposition (CVD), physical vapor deposition(PVD) and electroplating (for metallization and interconnect formation).

Conventional CVD processes require volatile precursors for the formationof precursor vapors that are transported to the chemical vapordeposition chamber. However, many chemical species are neither thermallystable enough, nor volatile enough, for sustained vaporization, deliveryand deposition. As a consequence, CVD processes for film deposition arelargely limited by the availability of volatile and stable precursors assource reagents.

PVD, utilizing a charged gas and a sputter target to effect depositionof material on a substrate, is well-developed and widely used in theart, but is limited by the significant particle levels that aregenerated in the process, as well as by constraints on controllabilityand conformality of the deposition process when tight geometries andsmall features are involved, and by process control issues relating todiffusion of the sputtered material. Due to the ballistic nature ofsputtered materials, it is extremely difficult to achieve conformalcoverage on complex topography of next generation patterned substrates.

Currently, many integrated circuit (IC) processes require low costdeposition of conformal thin-films for interconnect and dielectricstructures. The ability to deposit thin films, e.g., having a thicknessbelow about 1 μm, depends on the gas-phase transport of volatileorganometallic precursors that decompose at elevated temperatures ontopatterned substrates. Although many of such processes are extremelywell-developed for advanced microelectronic device manufacture, theapplication of these processes for high aspect ratio via filling isburdened by difficulties.

For deposition of conducting materials such as copper, CVD processestherefore can only compete with electroplating techniques (aqueous basedprocesses) when the cost of ownership (COO) for the process is small. Atdimensions of <0.1 micron, copper-porous low k multi-layers may requirespecial, non-aqueous processing to avoid aqueous contamination of thelow k pore structures and decreased device yields, and to enhance devicereliability. Further, the dielectric constant of the low k material iscritical and aqueous contamination can negatively increase dielectricconstants, which is largely unacceptable. Further, electroplatingrequires a conformal, conductive and uniform seed layer to enable thetechnique. The seed layer is deposited by PVD in conventional practice.With decreasing feature size and increasing aspect ratio, the use of PVDto obtain the required seed layers becomes a major technical challenge.Although ionized PVD conceivably could be useful for such purpose,alternative techniques are required, which are compatible with low kdielectrics.

The foregoing constraints and deficiencies of conventional semiconductormanufacturing deposition techniques reflect the need of the art forimproved process technologies that are free of such limitations.

SUMMARY OF THE INVENTION

The present invention relates to supercritical fluid (SCF)-assisteddeposition of materials onto substrates.

In one aspect, the invention relates to a deposition composition fordepositing material on a substrate, such deposition compositioncomprising a supercritical fluid and a precursor for the material to bedeposited on the substrate.

Another aspect of the invention relates to a method of forming amaterial on a substrate, comprising depositing the material on thesubstrate from a deposition composition comprising a precursor of suchmaterial, and a supercritical fluid.

Other aspects, features and embodiments of the present invention will bemore fully apparent from the ensuing disclosure and appended claims.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

Supercritical fluids are formed under conditions at which the density ofthe liquid phase equals the density of the gaseous phase of thesubstance. For example, carbon dioxide (CO₂), which is a gas at standardtemperature and pressure, undergoes a transition from liquid to SCFabove a critical point, corresponding to T_(c)≧31.1° C. and P_(c)≧73.8atm. Once formed, the density of the SCF can be varied from liquid-liketo gaseous-like, yielding different solvation abilities, by varying thepressure and temperature. Supercritical fluids have a solubility anddiffusibility approaching that of the liquid and gaseous phase,respectively. Additionally, the surface tension of SCFs is negligible.

Because of its readily manufactured character, ability to be recycled,lack of toxicity and negligible environmental effects, supercritical CO₂is a preferred SCF in the broad practice of the present invention,although the invention may be practiced with any suitable SCF species,with the choice of a particular SCF depending on the specificapplication involved.

The present invention relates to supercritical fluid-assisted depositionof thin-film (e.g., with a thickness of <1 μm) material on a substrate,e.g., a semiconductor wafer substrate.

Due to the progressively smaller dimensions of semiconductor patterns,the SCF-assisted deposition compositions of the present inventionprovide a distinct advantage in penetrating small geometry structuressuch as vias and trenches with high aspect ratios on a semiconductorwafer, as well as achieving improved homogeneity and extent ofconformality of the deposited material, e.g., in films, layers andlocalized material deposits, particularly in instances in which thewettability of the substrate is low, as is the case with manysemiconductor substrates.

The deposition compositions of the invention may be variously formulatedfor specific deposition applications, including suitable SCF(s) andsource reagent (precursor) compound(s), complex(es) and material(s).Such compositions may further optionally comprise co-solvent(s),co-reactant(s), surfactant(s), diluent(s), and/or otherdeposition-facilitating or composition-stabilizing component(s), asnecessary or desired for such applications.

In its simplest formulation, the deposition composition comprises atleast one SCF and at least one precursor component. The composition thuscomprises a supercritical fluid solution in which at least one precursorcomponent is dissolved.

The SCF precursor solution in use can be delivered to a heated substratefor contacting therewith, to deposit on the substrate a materialderiving from the precursor component(s). For example, the precursorcomponent may comprise a source reagent compound or organometallicspecies or metal coordination complex for forming a metal or dielectricfilm on a semiconductor wafer substrate.

By the use of SCF-based deposition compositions, the precursorcomponent(s) can be continuously delivered in a stream of the SCF-baseddeposition composition to the heated substrate, to deposit the desiredmaterial deriving from the precursor component(s) on the substratesurface. Concurrently, by-products of the deposition operation can becontinuously carried out of the deposition chamber via continuous flowof the SCF-based composition through the deposition chamber containingthe heated pedestal and substrate.

Alternatively, the deposition using the SCF-based deposition compositionmay be carried out in a batch mode, wherein the deposition compositionis contacted with the substrate, and process condition(s) (e.g.,temperature and/or pressure) of the composition are altered to effectthe deposition of the desired material deriving from the composition.

Examples of SCF species useful in the broad practice of the inventioninclude, but are not limited to, carbon dioxide, oxygen, argon, krypton,xenon, ammonia, methane, methanol, dimethyl ketone, hydrogen, forminggas, and sulfur hexafluoride.

Co-solvent or co-reactant species useful in the deposition compositionsof the invention may be of any suitable type. Illustrative speciesinclude, but are not limited to, methanol, ethanol, and higher alcohols,N-alkylpyrrolidones or N-arylpyrrolidones, such as N-methyl-, N-octyl-,or N-phenyl-pyrrolidones, dimethylsulfoxide, sulfolane, catechol, ethyllactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, γ-butyrolactone, butylene carbonate, ethylene carbonate,and propylene carbonate.

Surfactants useful in the deposition compositions of the presentinvention may likewise be of any suitable type, including anionic,neutral, cationic, and zwitterionic types. Illustrative surfactantspecies include, without limitation, acetylenic alcohols and diols, longalkyl chain secondary and tertiary amines, and their respectivefluorinated analogs.

The components of the SCF-based deposition compositions of the presentinvention may be present at any suitable concentrations and relativeproportions, as appropriate to the use of the composition in depositingmaterial on a substrate surface. For example, the precursor component(s)may be present at concentrations of from about 0.1% by weight to about98% by weight, with suitable concentrations being dependent on themaximum solubility of the precursor in the supercritical fluid that isemployed in the composition. For example, preferred concentration rangesof specific precursors may have any suitable minima (e.g., 0.2%, 0.5%,1%, 5%, or 8%), and maxima (e.g., 10%, 12%, 15%, 18%, 20%, 25%, 30%,40%, 50%, 60%, 75%, 80% or 90%), appropriate to the specificsupercritical fluid involved. As a further specific example, theconcentration of the precursor can be below about 40% when CO₂ is usedas the supercritical fluid in the SCF-based deposition composition. Theforegoing weight percentages are based on the weight of the SCF in thecomposition.

Further, the deposition compositions of the invention may selectivelycomprise, consist of, or consist essentially of, any of the SCF,precursor component(s) and optional additional components of thecompositions disclosed herein.

Deposition using the SCF-based deposition compositions of the inventionmay be carried out in any suitable manner, as regards contacting of thedeposition composition with the substrate. Chemical vapor depositiontechniques may be employed, or other modes of application of thedeposition composition to the substrate can be effected.

For example, in one approach, a polymeric or oligomeric precursorspecies is dissolved in a supercritical fluid to form the SCF-baseddeposition composition. This deposition composition in solution formthen can be sprayed into a fine mist or otherwise aerosolized. When themist or aerosol is transported onto the substrate surface, polymericfilms are formed. This technique is suitable for forming low k filmsfrom polymeric, oligomeric, pre-polymeric, or monomeric precursorcomponents, or combinations of same. In some applications, it isdesirable to transport the fluid media as a fine mist or aerosol to thesubstrate surface in a carrier fluid, or alternatively the compositionmay be delivered to the substrate in neat fluid, mist or aerosol form.

As another variant technique within the broad scope of the presentinvention, one or more precursor component(s) can be dissolved in asupercritical fluid, with the solution then being subjected to rapidexpansion. As a result of such rapid expansion, the precursorcomponent(s) are vaporized into fine vapor particles or nano-sizedaerosols (depending on the rapid expansion conditions), and such finevapor particles or aerosol can be used in CVD-type deposition processes.

The aforementioned techniques are useful for deposition of metals forinterconnect structures, as well as low k and high k dielectrics, andother materials and thin film compositions. Preferred supercriticalfluids for such purpose include carbon dioxide, methane, ethane,methanol, dimethyl ketone and sulfur hexafluoride.

The precursor components for the materials to be deposited on thesubstrate may be of any suitable type. Illustrative precursor componentsinclude, without limitation, organometallic source reagent compounds andcomplexes, and Lewis base adducts thereof, as well as the semiconductormanufacturing precursor components described in U.S. Pat. No. 5,840,897issued Nov. 24, 1998, U.S. Pat. No. 5,453,494 issued Jan. 18, 1994, U.S.Pat. No. 6,110,529 issued Aug. 29, 2000, U.S. Pat. No. 5,820,664 issuedMar. 31, 1995, and U.S. Pat. No. 5,225,561 issued Sep. 12, 1990, thedisclosures of all of which are hereby incorporated herein by reference,in their respective entireties.

The invention contemplates application of SCF-assisted deposition to anyof a wide variety of suitable techniques for depositing materials onsubstrates.

In one embodiment, SCF-assisted deposition is employed to enhancephysical vapor deposition (PVD) processes. In contrast to conventionalPVD techniques, which are conducted in an evacuated chamber, utilizing acharged gas and a sputter target for deposition of material on asubstrate, e.g., semiconductor wafer, the PVD process can be modified inaccordance with the present invention to utilize SCF-assisted depositiontechniques. Instead of a low-pressure system, a supercritical fluid,e.g., carbon dioxide and/or argon, or other SCF, is employed.

In carrying out such modified PVD process, it may be desirable toprovide an added Lewis base (e.g., PF3) or to conduct the deposition inthe presence of media such as CO, to form corresponding metal complexesin the PVD process. Illustrative examples of metal complexes of suchtype include, without limitation, Mo(CO)₆, W(CO)₆, Cr(CO)₆, W(PF₃)₆,CO₂(CO)₈, and CO₂(PF₃)₈.

By use of an SCF ambient environment in such modified PVD operation, areduced level of particle generation, improved control of depositioninto very tight geometries, improved control of diffusion of thesputtered material, and application of gas phase reactions in the PVDprocess (for forming barriers, or capping layers) are achievable,relative to conventional PVD techniques.

In another embodiment of the invention, low k films are formed usingalkyl silanes, siloxane precursors, and even organic-basednon-silicon-containing low k precursors, such as the low k dielectricthermosetting resin sold by The Dow Chemical Company under the trademarkSiLK. Silxoane precursors may be of any suitable type, as for examplealkyl siloxanes and cyclosiloxanes, such astetramethylcyclotetrasiloxane (TMCTS) and octamethyltetracyclosiloxane(OMCTS). Other low k film precursor materials can be utilized in theSCF-based deposition process of the present invention to form superiorfilms on substrates, without issues of adverse polymerization effects.

The deposition compositions of the invention therefore includecompositions wherein the precursor is a silicon source reagent, e.g., asiloxane in combination with an alkylsilane, e.g., trimethylsilane ortetramethylsilane. In another specific composition, the silicon sourcereagent comprises a siloxane, which is used in combination with aporogen, to form a porous low k film on the substrate.

The invention resolves a major deficiency of siloxane precursors thathas limited the utility of such materials for deposition applications.Specifically, the presence of even trace amounts of impurities in suchsiloxane precursors poses a risk of cationic or anionic polymerization,particularly at high temperatures, such as would otherwise result inpremature degradation in delivery lines to the deposition chamber. Forexample, TMCTS polymerizes in delivery lines at elevated temperatures,usually about 120° C., with potentially catastrophic consequences to thedeposition process and associated equipment.

Such premature degradation problems are overcome by SCF-based precursordelivery and deposition in accordance with the present invention.Supercritical fluid solutions of low k precursors are readily deliveredinto the growth chamber at low temperature, e.g., as low as 31.1° C.,due to the low viscosity of such solutions. Further, at the point thatthe pressure of the supercritical fluid solution is reduced, thesolution undergoes rapid expansion in volume, to vaporize the precursorinto a precursor vapor, with no ancillary heating requirement beingrequired.

Thus, the SCF-based deposition techniques of the invention, inapplication to low k film precursors, reduce thermally-inducedpolymerization of precursors such as siloxanes. More generally,thermally unstable low k film precursors of variant types areadvantageously delivered to the deposition substrate by SCF-basedcompositions. SCF species that are particularly useful for such purposeinclude carbon dioxide, methane, methanol, dimethyl ketone and sulfurhexafluoride.

In another aspect, SCF-based deposition compositions of the inventionmay be employed for precursor delivery to the substrate, to form barrierlayers, e.g., of TiN, TaN, NbN, WN or their corresponding silicides, orinterconnect and metallization structures, e.g., of copper, aluminum orother metals, metal alloys and species, on semiconductor substrates. Theprecursors for such purpose are dissolved in appropriate amounts in SCFmedia, and contacted with the heated substrate to effect deposition ofthe desired material.

For barrier layer formation, barrier layer precursor materials may be ofany suitable type for forming the aforementioned nitrides and silicides.Illustrative precursor components include, without limitation, titanium(IV) tetrakis-dialkylamides such as tetrakis diethylamido titanium(TDEAT), tetrakis dimethylamino titanium (TDMAT), and pyrozolatetitanium compounds and other titanium amido and imido compounds.Illustrative tantalum nitride (TaN) barrier precursor compounds include,without limitation, Ta (IV) pentakis(dialkylamido) compounds, such aspentakis ethylmethylamido tantalum (PEMAT), pentakis dimethylamidotantalum (PDMAT) and pentakis diethylamido tantalum (PDEAT), and theirW, Nb corresponding compounds.

Useful interconnect material precursors include, without limitation,metal beta-diketonate precursors, such as (hfac)Cu (I) Lewis baseadducts, as well as metal formates and metal acetates and their Lewisbase adducts.

For barrier layer or interconnect deposition applications, the SCF-baseddeposition composition can usefully contain optional co-reactants suchas ammonia (NH₃), hydrogen or other reducing co-reactants.

Barrier layer and metallization deposition applications can be carriedout in any suitable manner, as regards the deposition process. Forexample, the SCF-based deposition composition can be delivered onto thesubstrate surface in a continuous manner, to effect continuous filmgrowth on the substrate surface, with by-products of the depositionbeing carried away in the exhaust stream of supercritical fluid that isdischarged from the deposition chamber. Alternatively, the SCF-baseddeposition composition may be transported to a vaporizer, whereby thedeposition composition undergoes rapid expansion and vaporizes theprecursor component(s) into precursor vapor. Such vaporization may becarried out at very low temperature, e.g., room temperature, with theresulting precursor vapor being directed onto the heated substratesurface to grow the desired film thereon.

Since precursor components are in many cases quite reactive, theselection of supercritical fluid is important to ensure chemicalcompatibility of the deposition composition. The supercritical fluidsuseful for the aforementioned barrier layer and metallization depositioninclude, without limitation, CO₂, NH₃, CH₄, SF₆, N₂O, CO, and the like.

In a particular aspect of the present invention, SCF-based depositioncompositions are usefully employed for forming copper metallization onintegrated circuitry substrates. In such application, the supercriticalfluid facilitates a low surface tension, high-pressure technique fordeposition of copper thin films in deep trench and high aspect ratio viastructures.

Other applications of the invention include deposition of dielectricoxides.

As an important aspect of the present invention, deposition of metalthin films using SCF-assisted techniques in accordance with the instantinvention, relaxes the requirements for volatile metal precursors thatwould otherwise be necessary. By relaxing the requirement of volatilemetal precursors, the SCF-assisted deposition techniques of the presentinvention obviate the need for fluorine-functionalized precursors, whichare currently being increasingly used in the semiconductor manufacturingindustry to satisfy precursor volatility requirements. For SCF-assisteddeposition, the precursor component(s) need only be soluble in the SCFmedium in order to be transported to the deposition chamber andthermally decomposed onto the heated substrate.

In specific application to copper metallization, the invention permitsthe use of low-cost, non-volatile copper (I) and copper (II) precursorsfor deposition of thin film copper without the need forfluorine-containing precursors. This flexibility in turn eliminatesfluorine contamination on barrier surfaces and reduces electricalcontact resistances of inter-metallic layers, such as M1 to M2 copperlayers, and improves the adhesion of the copper film to nitridebarriers.

In accordance with the invention, copper may be deposited on a substratefrom SCF solution, utilizing a wide variety of non-volatile or lowvolatility copper precursors. Illustrative copper precursors include,without limitation, copper (II) β-diketonates, copper (II) carboxylates,copper (I) cyclopentadienes, copper (I) phenyls, copper (I) amides, andLewis base adducts of the aforementioned copper (I) and copper (II)species. A preferred supercritical fluid for such copper depositionapplications is carbon dioxide.

Since supercritical fluids exhibit liquid-like densities and gas-likeviscosities, having solvating properties similar to those of organicsolvents (e.g., pentane, hexane, and toluene), supercritical fluids candissolve many copper compounds that are soluble in organic solvents.Supercritical fluid solutions containing copper precursor(s) are easilydelivered to the film growth chamber for contacting with the substrateto deposit copper films thereon. Since surface tension is greatlyreduced by the SCF in the deposition composition, the copper precursoris effectively delivered into trenches and via openings with very highaspect ratios, to achieve superior conformal coating therein.

Copper precursor components usefully employed in the broad practice ofthe present invention for copper deposition include, without limitation,the following:

Cu (II) (β-diketonato)₂ species, such as Cu (II) (acac)₂, Cu (II) (thd)₂and Cu (tod)₂ as well as other non-fluorinated β-diketonate coppercompounds and complexes;

Cu (carboxylate)₂ species, such as Cu (formate)₂ and Cu (acetate)₂ andother long-chain (e.g., C₈-C₄₀ and more preferably from C₈-C₃₀)carboxylates. Cu (formate)₂ is a preferred copper source reagent becausethe formate ligand is able to act as a reducing agent, leading toultra-pure copper films upon thermal decomposition. Even highersolubility of copper formate in the SCF medium is obtainable bypolyamine complexation of Cu (formate)₂. Copper (II) carboxylates are apreferred copper precursor species, since such compounds are relativelyeasy to synthesize, utilizing low-cost starting materials. Suchcompounds have not heretofore been contemplated for use in copperdeposition applications, due to their poor volatility and poor transportcharacteristics, but are readily used for such purpose by formulation inSCF media in accordance with the present invention. As a result, thecost of ownership (COO) of copper deposition process systems isdecreased by the use of such low cost copper precursors.

(Cyclopentadienyl) CuL complexes (wherein L is a suitable ligandspecies), for example CpCu (I) PMe₃. Such precursors are fluorine-freeand are soluble in pentane and other organic solvents, and may beadvantageously utilized in the practice of the present invention.

Copper (I) phenyl tetramers, such as copper (I) pentafluorophenyl orcopper (I) t-butyl phenyl tetramer.

Copper (1) amides, such as bis(trimethylsilylamide) tetramer.

As alluded to above in respect of copper carboxylate precursors such ascopper formate, the present invention contemplates SCF-based depositioncompositions containing at least one copper precursor, wherein thecopper precursor contains a ligand that serves as a reducing agent forproduction of ultrahigh-purity copper films on the substrate.

As a further alternative, the SCF-based deposition composition cancomprise an SCF that is itself a reducing agent, or as a still furtheralternative, the SCF-based deposition composition can additionallyoptionally contain other reducing agent(s) for ensuring high puritycopper deposition on the substrate. Suitable reducing agents for suchpurpose may be readily determined without undue experimentation, withinthe skill of the art. Illustrative reducing species include, withoutlimitation, hydrogen and isopropyl alcohol.

In the SCF-based deposition compositions of the invention, variousenhancing agents and other beneficial components may be incorporated inthe composition.

For example, in SCF-based copper (II) precursor compositions, isopropylalcohol may be added in a concentration of from about 0.1% to about99.9% by weight, based on the weight of the SCF component(s). The use ofIPA as an enhancing agent is highly advantageous when the SCF componentis carbon dioxide, since isopropyl alcohol may increase copper precursorsolubility in the supercritical carbon dioxide, while simultaneouslyfunctioning as a reducing agent to reduce Cu (II) to Cu (O). Theisopropyl alcohol may be oxidized to acetone during the depositionprocess, and is readily recovered from the SCF effluent discharged fromthe deposition chamber, for recovery and reuse thereof, or alternativelyfor other disposition.

For copper deposition, the SCF can be of any suitable type, including,without limitation, CO₂, CH₄, C₂H₆, CH₃OH, C₂H₅OH, (CH₃)₂CHOH, CH₃COCH₃and SF₆.

The SCF-based copper precursor compositions of the invention afford ahighly effective approach to deposition of copper films on substrates.Such compositions may be employed in semiconductor manufacturingoperations as one of sequential deposition steps carried out in acluster tool for wafer processing.

It will be appreciated that the compositions and methods of theinvention may be practiced in a widely variant manner, consistent withthe broad disclosure herein. Accordingly, while the invention has beendescribed herein with reference to specific features, aspects, andembodiments, it will be recognized that the invention is not thuslimited, but is susceptible of implementation in other variations,modifications and embodiments. Accordingly, the invention is intended tobe broadly construed to encompass all such other variations,modifications and embodiments, as being within the scope of theinvention hereinafter claimed.

1.-165. (canceled)
 166. A deposition composition for depositing materialon a substrate, said deposition composition comprising a supercriticalfluid (SCF) and a siloxane in combination with one of an alkyl silane ora porogen.
 167. The deposition composition of claim 166, wherein the SCFcomprises a fluid selected from the group consisting of carbon dioxide,oxygen, argon, krypton, xenon, ammonia, methane, ethane, methanol,ethanol, isopropanol, dimethyl ketone, sulfur hexafluoride, carbonmonoxide, dinitrogen oxide, forming gas, hydrogen, and mixtures thereof.168. The deposition composition of claim 166, wherein the supercriticalfluid comprises carbon dioxide.
 169. The deposition composition of claim166, wherein the composition further comprises an additional componentselected from the group consisting of co-solvents, surfactants,co-reactants, diluents, deposition-enhancing agents, and combinationsthereof.
 170. The deposition composition of claim 166, wherein thealkylsilane comprises a species selected from the group consisting oftrimethylsilane and tetramethylsilane.
 171. The deposition compositionof claim 166, wherein the siloxane comprises a sub-species selected fromthe group consisting of alkylsiloxanes and cyclosiloxanes.
 172. Thedeposition composition of claim 171, wherein the siloxane comprises aspecies selected from the group consisting oftetramethylcyclotetrasiloxane (TMCTS) and octamethyltetracyclosiloxane(OMCTS).
 173. The deposition composition of claim 166, furthercomprising at least one co-solvent, wherein said co-solvent comprises asolvent selected from the group consisting of: methanol, ethanol,isopropyl alcohol, N-methylpyrrolidone, N-octylpyrrolidone,N-phenylpyrrolidone, dimethylsulfoxide, sulfolane, catechol, ethyllactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, γ-butyrolactone, butylene carbonate, ethylene carbonate,and propylene carbonate.
 174. The deposition composition of claim 166,further comprising at least one surfactant, wherein said at least onesurfactant comprises a species selected from the group consisting of ananionic surfactant, a neutral surfactant, a cationic surfactant, and azwitterionic surfactant.
 175. The deposition composition of claim 174,wherein said at least one surfactant comprises a surfactant selectedfrom the group consisting of acetylenic alcohols, acetylenic diols, longalkyl chain secondary and tertiary amines, and fluorinated derivativesof the foregoing.
 176. A deposition composition for depositing materialon a substrate, said deposition composition comprising a supercriticalfluid (SCF) and a metal precursor selected from the group consisting ofMo(CO)₆, W(CO)₆, Cr(CO)₆, W(PF₃)₆, CO₂(CO)₈, and CO₂(PF₃)₈.
 177. Amethod of forming a material on a substrate, comprising depositing thematerial on the substrate from a deposition composition comprising asupercritical fluid (SCF) and a siloxane in combination with one of analkyl silane or a porogen.
 178. The method of claim 177, wherein the SCFis selected from the group consisting of carbon dioxide, oxygen, argon,krypton, xenon, ammonia, methane, ethane, methanol, ethanol,isopropanol, dimethyl ketone, sulfur hexafluoride, carbon monoxide,dinitrogen oxide, forming gas, hydrogen, and mixtures thereof.
 179. Themethod of claim 177, wherein the composition further comprises anadditional component selected from the group consisting of co-solvents,surfactants, co-reactants, diluents, deposition-enhancing agents, andcombinations thereof.
 180. The method of claim 177, wherein thealkylsilane comprises a species selected from the group consisting oftrimethylsilane and tetramethylsilane.
 181. The method of claim 177,wherein the siloxane comprises a sub-species selected from the groupconsisting of alkylsiloxanes and cyclosiloxanes.